Autosomal dominant polycystic kidney disease (ADPKD) affects about 400,000 U.S. citizens and is the 3rd or 4th leading cause of kidney failure accounting for 8-10% of all diaysis patients. Acquired cystic disease (ACD) develops in over one-half of patients maintained on dialysis for 3 years or longer. In these and the rarer autosomal recessive PKD (ARPKD) cysts develop from renal tubules that may enlarge to many centimeters in diameter. Cyst enlargement is associated with the increased rate of growth of renal tubule epithelial cells. It is hypothesized that cysts develop and enlarge secondary to abnormal proliferation of tubule epithelial cells, and that reduction of epithelial proliferation will slow or stop cyst growth. The specific aims of this research are 1) to determine whether cell proliferation or fluid accumulation is the primary determinant of cyst enlargement; 2) to find candidate pharmacologic agents or extracellular conditions that will diminish epithelial cell proliferation in cysts and thereby slow cyst growth; 3) to determine the effects of the candidate pharmacologic agents and extracellular conditions on renal cyst dvelopment and growth, and on renal function in animals with hereditary and acquired renal cystic disroders; 4) to culture human cyst epithelial cells in vitro in order to determine the effect of candidate drugs and extracellular conditions on cell hyperplasia. Studies will be conducted in Madin-Darby canine kidney (MDCK) cells cultured within collagen or agarose gels to form cysts that progressively enlarge and fill with fluid as the cells proliferate. The rate of cell growth, cyst growth, transepithelial hydrostatic pressure, fluid pH,(Na), (K) and (Cl) will be determined following addition of candidate inhibitors of hyperplasia (e.g. amiloride, colchicine, hydroxyurea, increased (K) and decreased (Na). Cysts dissected from the Jackson C57 BL/6J cpk/cpk mouse and the Werder mouse (spontaneous diseases) and chemically acquired cystic diseases (diphenylthiazole, rat; methylprenisolone, neonatal rabbit) will also be studied in culture in the same format as MDCK cysts. Pharmacologic agents will be administered to mice, rats and rabbits with hereditary and acquired cystic disorders to determine the effect on cyst growth rate and renal function. Cell cycle analysis by flow cytometry will be performed on cells removed from cysts, and on cyst cells in culture. Successful completion of this research will justify the trial use of specific pharmacologic and dietary regimens in the treatment of human renal cystic disease.